Heart disease is the leading cause of death in the United States. A common and life-threatening complication of heart disease is myocardial infarction resulting from a thrombus that obstructs blood flow in one or more coronary arteries. The sooner thrombolytic medication such as tissue plasminogen activator (tPA) or urokinase is placed into the patient's bloodstream after the occurrence of an acute myocardial infarction, the sooner an obstructive thrombus will be dissolved and perfusion of the myocardium will be restored. The extent of damage to the myocardium is strongly dependent on the length of time that occurs prior to restoration of some blood flow to the heart muscle. At this time, no system exists that provides for early and automatic detection of an acute myocardial infarction and for rapidly providing the patient with a prescribed dose of a thrombolytic medication.
There are many patients who have implanted heart pacemakers or implanted cardiac defibrillators (ICDs). The purpose of the pacemaker is to provide a low energy electrical stimulation pulse that causes the heart to beat at a prescribed rate. The purpose of the defibrillator is to shock the heart back into sinus rhythm after ventricular fibrillation has been detected. However, no existing implantable pacemaker or defibrillator is also able to detect a partial or complete blockage of a coronary artery and warn the patient that this potentially fatal event is occurring. Furthermore, no pacemaker or ICD is presently used with an external communication and action system that rapidly responds to acute myocardial infarction or reversible myocardial ischemia that is detected by specially designed circuitry in that implanted pacemaker or ICD.
Although anti-tachycardia pacemakers and ICDs can detect heart arrhythmias and respond with electrical stimulation, none are currently designed to be part of a rapid response system designed to inform the patient as to his condition and to facilitate the injection of an anti-arrhythmic drug with a minimum time delay.
It is well known that an acute myocardial infarction can be detected from a patient's ECG by noting an ST segment deviation (i.e., voltage change) as compared to the voltage of the patient's TP or PQ segments. Such an ST segment deviation can be even more clearly discerned with electrodes implanted within the body (especially within or in close proximity to the heart) as compared with detecting the elevated ST segment from chest and/or limb mounted electrodes.
In U.S. Pat. Nos. 6,112,116 and 6,272,379 issued to R. E. Fischell, et al, an implanted cardiosaver system is described that includes an automatic delivery of medication when a heart attack is detected. These patents also teach the combination of internal and external alarm systems for informing the patient that a heart attack has been detected. However, the long term storage of any thrombolytic or anti-thrombogenic medication within a human patient can cause a deterioration of such drugs. Except for the treatment of an acute myocardial infarction, neither of these patents teaches how an external system could be used to treat any potentially fatal or at least worrisome cardiac event such as an arrhythmia and/or myocardial ischemia that is caused by an elevated heart rate resulting from physical effort including exercise.
In U.S. Pat. No. 5,479,780 by M. Zehender, a device is described that has a “goal of eliminating . . . cardiac rhythm abnormality.” In order to accomplish this goal, Zehender requires exactly two electrodes placed within the heart and exactly one electrode placed outside the heart. Although multiple electrodes could be used, an ideal sensor for providing an electrogram to detect a heart attack would use a single electrode placed within the heart. The Zehender patent teaches the detection of an ST segment deviation to indicate coronary ischemia and to use an implanted drug pump to release medication to treat such an ischemia. However, Zehender never discusses the treatment of acute myocardial infarction. Rather, the purpose of Zehender's invention is only to warn of an arrhythmia caused by myocardial ischemia. Zehender does not indicate that his invention could be used for the treatment of a heart attack. Furthermore, Zehender does not consider the problem of drug deterioration when such a drug is stored within an implanted device for later release when ischemia is detected. Still further, ischemia can result from exercise when there is progression of a stenosis in a coronary artery. Under such circumstances it would be highly undesirable to release a medication designed to treat the ischemia caused by a heart attack. Furthermore, Zehender does not describe an external system to be used in conjunction with an implanted cardiosaver device. Thus Zehender does not teach the use of an external alarm means or means to have a diagnostic center always on call for immediate diagnosis of a potentially fatal heart attack or arrhythmia. Furthermore, Zehender does not teach an implanted drug port that can be used for rapidly providing a bolus of medication from an external source to be delivered into a patient having a heart attack by either the patient himself, a caretaker of the patient or by a paramedic from an ambulance. Although Zehender does describe the use of a pacemaker or defibrillator in conjunction with an implanted device for detecting ischemia, he does not describe either an external alarm system to be used with the implant, nor does he describe the use of an implanted drug port to be used with the pacemaker or defibrillator.
The electrical signal from the heart as measured from electrodes within the body is called an a “electrogram”. The early detection of an acute myocardial infarction or myocardial ischemia caused by an increased heart rate or exertion is clearly feasible by using an implantable system that notes a change in a patient's electrogram. The implanted device portion of such a system is defined herein as a “cardiosaver” and the entire system including the implanted cardiosaver and the external portions of the system is defined herein as the “cardiosaver system.” Furthermore, although the masculine pronouns “he” and “his” are used herein, it should be understood that the patient or the medical practitioner who treats the patient could be a man or a woman. Still further the term; “medical practitioner” shall be used herein to mean any person who might be involved in the medical treatment of a patient. Such a medical practitioner would include, but is not limited to, a medical doctor (e.g., a general practice physician, an internist or a cardiologist), a medical technician, a paramedic, a nurse or an electrogram analyst. A “caretaker” is defined herein as a person that can come to the aid of the patient if the cardiosaver system indicates the occurrence of some cardiac related event such as a heart attack or ventricular fibrillation. A caretaker would include, but is not limited to, the patient's spouse, an attendant in a nursing home, a nurse or any person assigned to help take care of the patient. A “cardiac event” includes an acute myocardial infarction, ischemia caused by effort (such as exercise) and/or an elevated heart rate, bradycardia, tachycardia or an arrhythmia such as atrial fibrillation, atrial flutter, ventricular fibrillation, and premature ventricular or atrial contractions (PVCs or PACs). The use of this invention to treat stroke, will for the purposes of this specification, also be considered to be a “cardiac event”. For the purpose of this invention, the term “electrogram” is defined to be the signal from an implanted electrode that is placed in a position to indicate the heart's electrical activity.